This invention relates generally to recirculating systems for cleaning drilling muds. More particularly, the present invention relates to a desander/desilter mud cleaning system which combines the controlled multi stage use of centrifugal force and pressure for separating media of varying particle density.
As will be appreciated by those skilled in the industry, drilling muds are generally employed in the rotary drilling process as a medium for carrying solid cuttings such as sand, shale, and heavier rock particles recovered from the depths of the well to the upper surface of the earth. Because great volumes of mud are required for drilling and because the muds are generally quite expensive, it has become the common practice of those in the drilling industry to clean and reuse the drilling muds in order to maximize their economic benefit. The initial step in preparing the drilling muds for reuse involves the removal of the heavier materials recovered in drilling and the separation of the media of various density from the drilling mud. The present invention addresses itself principally to this initial stage of the cleaning process.
A number of prior art cleaning devices known to us demonstrate the employment of centrifugal force or a "cyclone" to create an interior vacuum which draws the lighter, more fluid drilling mud to the upper chambers of a suitable reservoir, leaving the heavier particles deposited at various levels therebelow. Mud-cleaning systems of this type are generally described in U.S. Pat. Nos. 2,274,503; 2,098,608; 4,216,095; and, 4,447,322.
U.S. Pat. Nos. 3,213,879 and 3,243,043 describe methods and mechanisms for regulating the discharge of solids from centrifuge separators. U.S. Pat. No. 4,462,899 describes a multiple chamber hydrocyclone cleaner assembly.
A more complex separator device which is adapted to separate gases and fine particles from the coarser materials recovered in deep rotary drilling is described by Freeman, U.S. Pat. No. 2,757,582. The Freeman device depends upon the downward, gravitational pull on the liquid medium as it passes through a vertical cone. A similarly vertically disposed cyclone separator is described in U.S. Pat. No. 2,756,878, which provides an additional outflow for separating out products of varying intermediate densities. Other relevant prior art devices known to us are presented in U.S. Pat. Nos. 2,723,750; 2,717,695; and 2,379,411, as well as my own separator invention defined in U.S. Pat. No. 4,431,535.
None of the prior art devices known to us, however, satisfactorily addresses problems commonly encountered in the desanding and desilting process. For example, "dirty" drilling mud returned to the surface may be constantly varying in the percentage, quality and content of contamination. The mud may contain at a given time a variety of recovered particles, liquid products, and gaseous materials of a wide range of density. The mud at one instant may be full of coarse sand, and shortly thereafter its content may change. Since the "quality" of the returned mud varies constantly, it is impractical to mechanically change between conventional desilters and desanders economically.
It is therefore desirable to provide multiple function separation means for distinguishing and separating out the materials of varying density from the single fluid drilling mud medium. None of the prior art devices are equipped to satisfactorily regulate the internal pressure of the various inner chambers for proper separation, which cannot be satisfactorily achieved through centrifugal force or gravity alone. By experimentation and experience with the product, it has become evident to me that a suitable separator should provide a number of independent cleaning chambers adapted to continuously process the recovered mud in such a way as to provide an output of uniform consistency notwithstanding the fact that the incoming raw or "dirty" mud may constantly vary in quality.